SLOVYANSK, UKRAINE - APRIL 24: Pro-Russian separatist militants fill sand bags to reinforce a checkpoint on April 24, 2014 in Slovyansk, Ukraine. Pro-Russian activists have been occupying government buildings and demanding greater autonomy in many Eastern Ukrainian cities in recent weeks, prompting the government in Kiev to threaten military action to retake control of the cities. (Photo by Brendan Hoffman/Getty Images) *** Local Caption ***